The present invention relates to an arrangement for transporting web-shaped materials, particularly phosphor foils and/or X-ray sheet films, which can be stimulated, at a constant transporting speed in an apparatus for scanning and/or exposing these materials.
Arrangements of the above mentioned general type are known in the art. One such known arrangement is disclosed in the U.S. Pat. No. 4,831,461 and includes a transporting roller unit and a drive unit for driving the transporting roller unit and therefore transporting a web-shaped material,. The uniformity of the transport speed required in an apparatus for scanning and/or exposing phosphor foils and/or X-ray sheet films which can be stimulated is achieved in this patent by a regulated drive motor and by various constructional steps in the design of the transporting roller unit. For example, it is achieved by lifting of a feed roller of the transporting roller pair when the front edge of the film is drawn in by the transporting roller pair, by means of a control device which detects the front edge of the film. Also, this is done by resilient feed rollers, a minimum spacing between the rollers of the transporting roller pair, a spring mounted feed roller so that the transporting roller pair can be pressed away by the web-shaped material. For rotational movement of the drive motor is transmitted to a first transporting roller pair directly or through a belt composed of metal or plastic. The second transporting roller pair is connected with the first transporting roller pair by belts or additional rollers and discs, respectively, and rotate synchronously with the first transporting roller pair. Since in this patent the drive motor is connected with the transporting rollers to be driven directly or via a drive belt composed of metal or plastic, the above-mentioned constructual steps or their combination are necessary in order to maintain a low alternation of load when the film edges enter or exit the transporting roller pair. In addition to this step which is costly itself it is necessary to regulate the drive motor in order to achieve a constant transporting speed.